Rotary fluid pressure device and pressure relief system therefor

ABSTRACT

A rotary fluid pressure device includes a housing having a fluid inlet port and a fluid outlet port and defines a fluid sealing surface therein. An internally-toothed member is provided, and an externally-toothed member is eccentrically disposed therein for relative orbital and rotational movement. The teeth of the members interengage to define a plurality of expanding and contracting volume chambers during the relative movement therebetween. A valve means is connected for synchronous movement with either the orbital or rotational movement of one of the toothed members to connect one of the fluid ports in fluid communication with the expanding volume chambers and the other fluid port in fluid communication with the contracting volume chambers. Each of the toothed members has an axial end face disposed in engagement with a portion of the sealing surface defined by the housing. The sealing surface and one of the axial end faces cooperate to define a sealing land radially adjacent the volume chambers, and at least one area of relieved pressure, the sealing land being disposed radially between the volume chambers and the relieved area. A passage means is disposed within the housing for connecting the relieved area in open communication with whichever one of the fluid ports is at a lower fluid pressure to reduce the area between the sealing surfaces and end faces subjected to fluid pressure, to thereby reduce the force tending to separate the end face from the adjacent sealing surface during operation of the device.

United States Patent [191 Swedberg [451 Sept. 16, 1975 ROTARY FLUID PRESSURE DEVICE AND PRESSURE RELIEF SYSTEM THEREFOR Nils Einar Swedberg, Chanhassen, Minn.

[75] Inventor:

[52] US. Cl 418/61 B; 418/81; 418/149; 418/270 [51] Int. Cl. F01C 1/02; F01C 21/00; F03C 3/00; F04C 1/02 [58] Field of Search 418/61 B, 75, 80, 81, 149, 418/270; 60/384 [56] References Cited UNITED STATES PATENTS 1,894,353 l/1933 Kempton 418/149 3,289,542 12/1966 Fikse 418/61 B Hansen...

White.....

Primary ExaminerJohn J. Vrablik Attorney, Agent, or Firm-Teagno & Toddy 5 7 I ABSTRACT A rotary fluid pressure device includes a housing having a fluid inlet port and a fluid outlet port and defines a fluid sealing surface therein. An intemally-toothed member is provided, and an externally-toothed member is eccentrically disposed therein for relative orbital and rotational movement. The teeth of the members interengage to define a plurality of expanding and contracting volume chambers during the relative movement therebetween. A valve means is connected for synchronous movement with either the orbital or rotational movement of one of the toothed members to connect one of the fluid ports in fluid communication with the expanding volume chambers and the other fluid port in fluid communication with the contracting volume chambers. Each of the toothed members has an axial end face disposed in engagement with a portion of the sealing surface defined by the housing. The sealing surface and one of the axial end faces cooperate to define a sealing land radially adjacent the volume chambers, andat least one area of relieved pressure, the sealing land being disposed radially between the volume chambers and the relieved area. A passage means is disposed within the housing for connecting the relieved area in open communication with whichever one of the fluid ports is at a lower fluid pressure to reduce the area between the sealing surfaces and end faces subjected to fluid pressure, to thereby reduce the force tending to separate the end face from the adjacent sealing surface during operation of the device.

27 Claims, 10 Drawing Figures Tin 19 PATENTED SEP I 8 I975 SFEU 1 OF PATENTED SEF I 6 I975 sum 2 05 PATENTED SEP l 8 I975 SHEET L, 0F

139 I2 has qa'rl I97 NOT RELIEVED RELIEVED SEALING FIG. 6

PSI.

FIG. 7

ROTARY FLUID PRESSURE DEVICE AND The present invention relates to rotary fluid pressure devices, especially of the orbiting type, and more par ticularly, to such devices having a fluid pressure relief system for improved axial sealing.

While the present invention is equally applicable to many types of rotary fluid pressure devices, it is especially adapted for use with fluid pressure motors, pumps and servocontrol units of the orbiting type, and will be described in connection therewith. Hydraulic devices of the class described are generally characterized by a gerotor set including an externally-toothed member eccentrically disposed within an intemallytoothed member, with relative rotational and orbiting motion between the toothed members. A splined universaljoint drive arrangement is commonly used to translate the rotational component of the movement of the extemally-toothed membereither to or from a journalled output or input shaft, depending upon whether the device is being used, respectively, as a motor or as a pump. The relative motion of the toothed members defines a plurality of volume chambers therebetween, each of the volume chambers alternately expanding and contracting in response to the relative motion. A rotatable valving means is usually associated with the gerotor set to selectively port fluid to and from the volume chambers, for example, high pressure fluid to the expanding volume chambers and low pressure fluid from the contracting volume chambers when the device is being used as a motor.

Typically, rotary fluid devices of the gerotor type utilize hydraulic pressures in the range of about 1,000 psi to about 4,000 psi. Such pressures result in high separating forces acting on the end faces of the axial sealing members disposed on either side of the gerotor set. Such separating forces can cause stretching of the tie bolts and deflection of axially adjacent sealing surfaces, allowing excessive leakage to occur in the planes between the gerotor set and the adjacent sealing members and further to cause seal ring failures allowing external leakage to occur as a result of the stretched tie bolts. Deflection of the axially-adjacent sealing members may also permit excessive internal leakage of high pressure fluid, either to the case or to where there is a low fluid pressure. Such leakage detracts from the work output of the hydraulic pump ormotor and-represents volumetric inefficiency of the device. In devices such as motors and pumps where some of the volume chambers contain high pressure fluid and some contain low pressure fluid, deflection of a sealing member in sliding contact with a portion of the gerotor set, such as the externa lly-toothed member, can result in uneven wear characteristics between the sliding members, often reducing the operable life of the device.

Prior art attempts at overcoming the problems associated with high internal separating forces, sealing member deflection and internalleakage have generally involved increasing the sealing area or increasing the axial sealing force by either increasing the strength of the tie bolts and/or providing axial-pressure balancing. Balancing the axial pressure of the. sealing members against the gerotor seti ha's frequently been accomplished by porting hydraulic pressure into areas behind the sealing members, as is illustrated generally US. Pat.

Nos. 3,034,448 and 3,694,114. In another approach to the problem, as illustrated in US. Pat. No. 3,695,791, the gerotor set is disposed between a pair of sealing members which are either pressure sensitive, temperature sensitive, or both, so that the clearances between the sealing members and the gerotor set is permitted to vary in accordance with changing pressure or temperature conditions. These eflorts to overcome the aforementioned problems have not been fully satisfactory.

SUlVflVlARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a rotary fluid pressure device having improved voltunetric efficiency, especially at low speeds and high hydraulic pressures.

It is a more specific object of the present invention to provide such a device in which there is a reduction in the internal leakage caused by deflection of the sealing members in sliding engagement with a portion of the gerotor set.

It is an even more specific object of the present invention to provide an orbiting hydraulic device having areas of relieved fluid pressure adjacent the volume chambers and defining a sealing land therebetween to reduce the effective area over which leaking, high pressure fluid exerts a separating force on adjacent members, thus reducing the total axial separating force acting on these members.

It is another object of the present invention to provide an orbiting hydraulic device of the type including a sealing member in sliding engagement with a portion of the gerotor set wherein axial deflection of the sealin g member is minimized to decrease leakage and improve the wear characteristics between the sealing member and the gerotor set.

These and other objects of the present invention, which will become apparent upon a reading of the following detailed description, are accomplished by the provision of an improved rotary fluid pressure device of the type described including a housing having a fluid inlet port and a fluid outlet port and defining a sealing surface therein; an internally-toothed member and and externally-toothed member eccentrically disposed therein for relative orbital and rotational movement therebetween. The teeth of the members interengage to define a plurality of expanding and contracting volume chambers during the relative movement. There is also provided a valve means and a means connecting the valve means for synchronous movement with one of the movements of one of the toothed members, the valve means being operable upon the synchronous movement to connect one of the ports in fluid communication with the expanding volume chambers and the other port in fluid communication with the contracting volume chambers. The toothed members have axial end faces abuttingly engaging the sealing surface, the sealing surface and one of the end faces cooperating to define a sealing land radially adjacent the volume chambers and at least one area of relieved pressure, the sealing land being disposed radially between the volume chambers and the area of relieved pressure. A passage means is disposed within the housing for connecting the relieved area in open communication with one of the ports, to reduce the area subjected to fluid pressure tending to separate the axial end faces from the sealing surface during operation of the device.

In accordance with another aspect of the present invention, a seal ring groove is included and the sealing land is disposed radially between the volume chambers and the seal ring groove and the area of relieved pressure is in open communication with the seal ring groove.

In accordance with still another aspect of the present invention the area of relieved pressure may comprise a fluidically continuous groove disposed generally concentric with the seal ring groove, or may comprise a plurality of circumferentially spaced apart relieved areas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional view of a rotary fluid pressure device utilizing the present invention.

FIG. 2 is a transverse cross-sectional view taken on line 2-2 of FIG. 1.

FIG. 3 is a transverse cross-sectional view taken on line 33 of FIG. 1.

FIG. 4 is a transverse cross-sectional view taken on line 44 of FIG. 1.

FIG. 5 is a transverse cross-sectional view, of the valve member only, taken on line 55 of FIG. 1.

FIG. 6 is a hydraulic pressure diagram comparing devices with and without pressure relief.

FIG. 7 is a graph illustrating volumetric efficiency with and without pressure relief.

FIG. 8 is a longitudinal cross-sectional view of an alternative embodiment of the present invention.

FIG. .9 is a transverse cross-sectional view taken on line 99 of FIG. 8.

FIG. 10 is a transverse cross-sectional view taken on line 1010 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, which are for the purpose of illustrating preferred embodiments of the present invention, and not for limiting same, FIG. 1 is a cross-sectional view of a typical rotary fluid pressure device of the type with which the present invention may be advantageously utilized. More specifically, FIG. lshows a hydraulic motor of the orbiting or gerotor type, it being understood that the term motor when applied to such fluid pressure devices also is intended to encompass the use of such devices as pumps. The hydraulic motor, generally designated 11, comprises a plurality of sections secured together, including, from front to rear respectively, a shaft support casing 13, a wear plate 15, a gear set or gerotor set 17, a valve port plate 19, and a valve casing 21. The basic construction and operation of the motor 11 is known to those skilled in the art and may be understood by reference to US. Pat. No. 3,572,983, the specification of which is incorporated herein by reference.

The gerotor set 17, shown in greater detail in FIG. 3, is known in the art and will therefore by described only briefly as it pertains to the structure and operation of the present invention. The gerotor set 17 comprises an intemally-toothed member 23 including, in the subject embodiment, seven teeth 25, and eccentrically disposed within the member 23, an externally-toothed member 27 having, in the subject embodiment, six teeth 29. The eccentric disposition of externallytoothed member 27, as well as the difference in the numbers of teeth, permits member 27 to orbit within member 23 while rotating. Itshould be clearly understood that either member 23 or member 27 may be relatively fixed, while the other member orbits and rotates with respect thereto. The combination of relative orbital and rotatational movement causes the interengagement of teeth 25 and teeth 29 to define a plurality of circumferentially spaced volume chambers 31, 33, 35, 37, 39, 41 and 43, which alternately expand and contract.

Referring again to FIG. 1, the motor 11 includes an input-output shaft 45 positioned within shaft support casing 13 and spaced therefrom by bearing sets 47 and 49. The shaft 45 includes internal splines 51 and in engagement therewith is a main drive shaft 53 having sets 55 and 57 of crowned involute teeth at opposite ends thereof. The involute teeth 57 are in engagement with splines 59 of externally-toothed member 27. Therefore, in the subject embodiment, seven orbits of member 27 result in one complete rotation thereof, and one rotation of input-output shaft 45. Also in engagement with splines 59 is a set of teeth 61 about the periphery of valve drive shaft 63. At the opposite end of shaft 63 is a set of teeth 65, and in engagement with internal splines 71 of a valve member 73, rotatably disposed within valve casing 21. The casing 21 includes a pair of fluid ports 75 and 77, and as illustrated herein, port 75 is for high pressure fluid and port 77 is'for low pressure fluid, with the device being subsequently described for use as a motor, i.e. high pressure fluid entering the de-. vice through port 75, causing rotation of shaft 45, and being exhausted from the device at low pressure, through port 77.

Referring now to FIG. 5, in conjunction with FIG. 1, the valve member 73 includes an alternating arrangement of high pressure valve passages 81, 83, 85, 87, 89 and 91 and low pressure valve passages 93, 95, 97, 99, 101, and 103. It should be noted that each of these passages remains either at high pressure or a low pressure continually during the operation of the device.

FIG. 4 illustrates the valve port plate 19 including the port passages 105, 107, 109, 111, 113, and 117, each of which is alternately in and out of communication with the valve passages of valve member 73 during rotation thereof. With the device momentarily in the position as shown in FIGS. 3, 4, and 5, and the extemally-toothed member 27 rotating clockwise, high pressure fluid is fed through valve passages 81, 83, and 85, through port passages 105, 107, and 109 and into volume chambers 31, 43 and 41, causing the chambers to expand. Port passage 111 and its associated volume chamber 39 contain fluid which is at a pressure somewhere between high pressure and low pressure, and therefore passage 11] and chamber 39 are referred to as being in a changeover condition. At the same time, volume chambers 33, 35 and 37 are contracting, forcing low pressure fluid out of the chambers, through port passages 113, 115 and 117 into low pressure valve passages 101, 103 and 93. g v

Referring again to FIG. 1, the gerotor set 17, containing pressurized fluid, is abuttingly engaging sealing surfaces defined by the housing, i.e. the members 15 and 19 adjacent the gerotor set. Specifically, internallytoothed member 23 has axial end faces 121 and 123 in engagement, respectively, with sealing surface 125 of wear plate 15 and sealing surface 127 of valve port plate 19. Similarly, externally-toothed member 27 has axial end faces 131 and 133 in engagement, respectively, with sealing surfaces 125 and 127. As discussed previously, the deflection of end faces and sealing'surfaces can cause internal leakage of fluid, for example, between high pressure areas chambers and lowpressure volume chambers in gerotor set 17. In addition, deflection of valve port plate 19 can cause separation between its face and the adjacent face of valve member 73, thus permitting a short circuit type of fluid leakage between high pressure valve passages and adjacent low pressure valve passages. As is shown in FIG. 1, hydraulic fluid is prevented from leaking out of the device in a radially outward direction by sealing means such as O-rings or the like disposed in seal ring grooves 135, 137, 139 and 141.

As can best be seen in FIGS. 2 and 3, in conjunction with FIG. 1, there is a plurality of depressions or apertures defined in axial end face 121 and sealing surface 125, the depressions providing pressure relief areas 143, 145, 147, 149, 151, 153 and 155. At the opposite end of gerotor set 17, axial end face 123 and sealing surface 127 similarly define a plurality of apertures or depressions, and as best shown in FIG. 4, the depressions provide pressure relief areas 157, 159, 161, 163, 165, 167 and 169. In the subject embodiment, pressure relief areas 143-155 are in fluid communication with seal ring groove 137 while pressure relief areas 157-169 are in fluid communication with seal ring groove 139, both of which are placed in fluid communication with low pressure fluid port 77 by means of passage 171.

Referring again to FIG. 3 wherein seal ring groove 137 as well as pressure relief areas 143-155 are shown in dotted line form, the function of the pressure relief areas will be better understood. Note that each of the pressure relief areas 143-155 is disposed adjacent and radially outward from one of the volume chambers 31-43. Referring now to FIG. 6, in conjunction with FIG. 3, a fragmentary cross-section is shown, similar to FIG. 1, but taken through the volume chamber 31, rather than through tooth 25. There is shown in FIG. 6 a hydraulic pressure diagram comparing a device of the type disclosed herein which is not relieved, i.e. includes only seal ring grooves 137 and 139, with a device including pressure relief as taught herein. In the not relieved device, the high pressure fluid contained in volume chamber 31 is leaking between axial end face 121 and sealing surface 125, therefore exertinga separating force equal to the area under the graph, ie between the HIGH" pressure line and the LOW pressure line. The addition of the pressure relief areas 143-155 results in the sealing surface 125 and end face 121 defining a sealing land 173, which is the area between volume chamber 31 and pressure relief area 155 over which sealing surface 125 and end face 121 are in contact or in engagement. As can be seen on the hydraulic pressure diagram for the relieved device, the porting of the seal ring groove 137 and the pressure relief areas 143-155 to the low pressure fluid port 77 results in a pressure drop from high pressure to low pressure across the relatively narrow sealing land 173. This, in turn, greatly reduces the area over which the high pressure fluid exerts a pressure tending to separate surface 125 from end face 121. In each case, it should be noted that the maximum pressure is the same. However, the total area over which this pressure is allowed to act is greatly reduced in the device incorporating the relieved areas of the present invention, thereby greatly reducing the total separating force (area under the graph). Although it will be understood that the drawing figures are included for the purpose of illustrating the invention, and not for representing relative dimensions, it has been found preferable to make the pressure relief areas 143-155 of a size such that their total area is relatively greater than the area of the sealing land 173, with the sealing land 173 generally being relatively narrower in a radial direction than the adjacent area of relieved pressure.

FIG. 7 is a graph of volumetric efi'iciency versus the operating pressure in PSI of the hydraulic fluid. The test was performed with a pair of high torque, low speed hydraulic motors of the type disclosed herein and made by the Char-Lynn Plant of Eaton Corporation. One of the motors had no pressure relieved areas (NR) and the other had relieved areas (R) in accordance with the invention. A Mobile oil (type DTE 26) was used at an oil temperature of F and a viscosity of 117 ssu. The motors used in the test had a 4.5 cu. in. displacement and the input flow rate of the hydraulic fluid was about 5 GPM (gallons per minute). The sym bols CW and CCW indicate, respectively, clockwise and counterclockwise rotation of the gerotor set. As can be seen from the graph of FIG. 7, a substantial im provement in volumetric efficiency can be achieved using the teachings of the present invention. For example, at 3500 psi the pressure relief disclosed herein improved the volumetric efficiency from about 68 to about 84 percent in the clockwise direction and from about 78 to about 91 percent in the counterclockwise direction, yielding improvements, respectively, of about 16 and about 13 percent.

In FIGS. 8, 9 and 10 there is illustrated an alternative embodiment of the present invention in which the fluid pressure device is a servo-control unit, generally desig nated 201, of the type commonly used to meter hydraulic fluid to a pressure cylinder of a power steering system. The control device 201 includes a housing section 203, a valve port plate 205, a metering element or gerotor set 207, and an endcap member 209. These sections are fastened in tight engagement by a plurality of tie bolts 211 passing through axially extending bores 213. Rotatably disposed within the housing 203 is a rotary input valve member or spool 215. The valve member 215 has, at its forward end, internal splines 217 for connection to an externally splined steering column shaft (not shown). Disposed between the valve member 215 and the housing 203 is follow-up valve member or sleeve 219 which is connected for limited rotational movement relative to valve member 215 by means of the drive pin 221 and a slot arrangement in the members 215 and 219 which is better shown in US. Pat. Re 25,126 and forms no part of the present invention. The drive pin 221 passes through a slot in drive shaft 223 and provides a rotational input thereto, the shaft 223 terminating in a splined head 225.

The metering element or gerotor set 207 includes an internally-toothed member 227 and, eccentrically disposed therein, and externally-toothed member 229 having internal splines 231 in engagement with the splined head 225. The construction and operation of devices such as servo-control unit 201 are well known in the art and may be better understood by reference to US. Pat. No. Re 25,126 which is incorporated herein by reference.

The rotation of the steering column displaces valve member 215, relative to valve member 219, thereby ,ther direction, hydraulic fluid is introduced into the device through an inlet port and flows through the various valve passages defined by housing 203 and valve members 215 and 219. This incoming hydraulic fluid is fed through valve port plate passages 247, 249 and 251 into volume chambers 245, 243 and 241, respectively. Valve port plate passage 253 is in fluid communication with volume chamber 239 which is a changeover cham- I ber when in the position shown in FIG. 10, as described in connection with the embodiment of FIGS. 1 7. As is shown by the arrow in FIG. 10, the extemallytoothed member 229 is rotating in a clockwise direction with the result that hydraulic fluid flows from volume chambers 237, 235 and 233 through valve port plate passages 255, 257 and 259, respectively. This fluid then passes through certain of the valve passages to either the right turn outlet or the left turn outlet, depending upon the direction of rotation of the steering wheel.

The internally toothed member 227 has an axial end face 261 and externally-toothed member 229 has an axial end face 263, the end faces 261 and 263 engaging a sealing surface 265 of valve port plate 205. At the opposite end of the gerotor set 207, internally-toothed member 227 has an axial end face 267 and externallytoothed member 229 has an axial end face 269, the end faces 267 and 269 engaging a sealing surface 271 of endcap member 209. The valve port plate 205 has a second sealing surface 273 oppositely disposed from the sealing surface 265, and in engagement with a sealing surface 275 of the housing 203. Surfaces 273 and 275, face 261 and surface 265 and. face 267 and surface 271 define, respectively, seal ring grooves 277, 279 and 281 in which O-rings or the like are disposed. Disposed radially inward from seal ring grooves 277, 279 and 281 are, respectively, pressure relief grooves 283,285 and 287. As is best seen in FIGS. 9 and 10, the pressure relief grooves 283, 285 and 287 are fluidic ally continuous and, as. shown in FIG. 8, are interconnected by fluid passage means 289 comprising the clearance 291 between each of the bores 213 and the tie bolt 211 received therein. Referring again to FIG. 10, it will be appreciated that the improved relieved area structure of the alternative embodiment functions in a manner similar to the embodiment of FIGS. 1-7. The pressure relief groove 285 defined by axial end face 261 and sealing surface 265 (see FIG. 8) is disposed radially outward from the volume chambers 233-245, so that each segment of the pressure relief groove 285 and the adjacent volume chamber defines a portion'of a narrow sealing land 293- therebetween. Here it should'be noted that fluid in the expanding and contracting chambers is at approximately the same fluid pressure and both are at a substantially higher pressure than the fluid which is permitted to pass from the device through a fluid exhaust, port. Therefore, a pressure drop occurs, in a manner similar to that shown in FIG. 6, from the volume chambers to the pressure relief groove, in a radially outward direction across the sealing land 293.

In FIG. 8, there is shown between axial end face 263 and sealing surface 265 an optional pressure relief area 295 which is radially inward of the bottom of the teeth on externally-toothed member 227, and which, in the same manner as described previously, provides a pressure drop across a relatively narrower sealing land defined by the outer periphery of member 229 and the outer periphery of relief area 295. Similarly, a pressure relief area 297, also shown in dotted line form in FIG. 10, is defined by axial end face 269 and sealing surface 271. Finally, between sealing surfaces 273 and 275 there is an inner pressure relief groove 299 which functions in the same manner as pressure relief areas 295 and 297. Also shown is a radial groove 301 which permits leaking hydraulic fluid to flow from pressure relief grooves 285 and 287 through clearances 291 around pressure relief groove 283 and along radial groove 301 to the internal cyclindrical bore 303 defined by wear plate 205 and valve member2l5. From bore 303 the fluid then passes to the exhaust port, from which it returns to the reservoir tank (not shown).

. In connection with the foregoing description it will be understood by those skilled in the art that the illustration of a depresssion, recess or groove being formed in a particular member is intended, within the scope of the present invention, to include the forming of such depression, recess or groove in the adjacent, engaging member, or jointly between the adjacent members, or of any other fluidically equivalent arrangement.

The invention has been described in great detail sufficient to enable one of ordinary skill in the art to make and use the same. Obviously, modifications and alterations of the preferred embodiments will occur to others upon a reading and understanding of the specification and it is my intention to include all such alterations and modifications as part of my. invention insofar as they come within the scope of the appended claims.

I claim:

1. A rotary fluid pressure device, comprising:

a. a housing having a fluid inlet port and a fluid outlet port and defining atleast a first surface therein;

. b. an intemally-toothed member and an extemallytoothed member eccentrically disposed within said internally-toothed member for relative orbital and rotational movement therebetween, the teeth of said members interengaging to define a plurality of expanding and contracting volume chambers during said relative movement;

c. valve means;

-d. means connecting said valve means for synchronous movement one of said movements of said toothed members, said valve means being operable upon said synchronous movement to connect one of said ports in fluid communication with said expanding volume chambers and the other of said ports in fluid communication with said contracting .volume chambers,

e. said toothed members having first axial end faces abuttingly engaging said first housing surface, said housing surface and one of said first axial end faces cooperating to define a first sealing land radially adjacent said volume chambers and at least one area of relieved pressure, including a fluidicly continuous groove, said sealing land being disposed radially between said volume chambers and said area of relieved pressure; Y

f. said area of relieved pressure being at least about as wide in a radial direction as said sealing land;

and

g. passage means disposed within said housing for connecting said relieved area in open communication with one of said ports to reduce the area subjected to fluid pressure tending to separate said faces from said surface during operation of said device. a

2. The device of claim 1 wherein said sealing land has a generally constant width and is substantially continuous circumferentially about said first housing surface.

3. The device of claim 1 including a plurality of circumferentially spaced apart areas of relieved pressure, the total of said relieved areas being relatively greater than the area of said sealing land.

4. The device of claim 1 wherein said fluidicly continuous groove comprises a seal ring groove and sealing means disposed therein, said sealing land being disposed radially between said volume chambers and said seal ring groove.

5. The device of claim 1 including a generally circular seal ring groove disposed generally concentric with said fluidicly continuous groove.

6. The device of claim 1 wherein:

a. said housing defines a second surface therein, said first and second surfaces being substantially parallel and oppositely disposed about said toothed members; and

b. said toothed members having second axial end faces abuttingly engaging said second housing surface, said housing surface and one of said axial end faces cooperating to define a second sealing land radially adjacent said volume chambers and at least one second area of relieved pressure, said second sealing land being disposed radially between said volume chambers and said second relieved area.

7. The device of claim 6 wherein said first and second relieved areas are inopen communication.

8. A rotary fluid pressure device, comprising:

a. a housing having a fluid inlet port and a fluid outlet port;

b. an internally-toothed member having first and second axial end faces thereon and an externallytoothed member eccentrically disposed within said intemallytoothed member for orbital and rotational movement relative thereto, the teeth of said members interengaging to define a plurality of expanding contracting volume chambers during said relative movement;

c. valve means operable between said inlet port arid said outlet port for selectively porting fluid to and from said volume chambers as said chambers alternately expand and contract in response to said relative movement; I

d. means connecting said valve means for synchronous movement with one of said movements of said toothed members; i

e. a first plate member having an axial end face in engagernent withsaid firstaxial end face of said internally-toothed member over; a 1 major portion thereof; i

f. said plate member end face and said first axial end face cooperating to define a first sealing land disposed radially outward from and adjacent to said volume chambers and at least one area of relieved pressure including a fluidicly continuous groove disposed radially outward from and adjacent to said sealing land;

g. said area of relieved pressure being at least about as wide in a radial direction as said sealing land; and

h. passage means disposed within said housing for venting said relieved area to reduce the pressure therein, to thereby reduce the force tending to separate said end faces during pressurization of said volume chambers.

9. The device of claim 8 wherein said fluidicly continuous groove comprises a seal ring groove and sealing means disposed therein.

10. The device of claim 8 including a generally circular seal ring groove, said fluidicly continuous groove being generally circular and disposed concentric with said seal ring groove.

11. The device of claim 8 including a plurality of said area of relieved pressure, each of said areas being disposed radially outward from and adjacent to one of said volume chambers and disposed circumferentially between adjacent teeth of said internally-toothed member.

12. The device of claim 11 wherein the total of said relieved areas is relatively greater than the area of said sealing land to minimize the area over which leakage of pressurized fluid can exert a force tending to separate said engaging end faces.

13. The device of claim 12 wherein said sealing land has a generally constant width and is substantially continuous circumferentially about said internally-toothed member.

14. The device of claim 8 including:

a. a second plate member having an axial end face in engagement with said second axial end face of said internally-toothed member over a major portion thereof;

b. said second plate member end face and said second axial end face cooperating to define a second sealing land disposed radially outward from and adjacent to said volume chambers and at least one second area of relieved pressure radially outward from and adjacent to said sealing land; and

c. said relieved area being in fluid communication with said passage means.

15. The device of claim 14 wherein a plurality of fluid passage means extend axially through said intemallytoothed member interconnecting said first and second areas of relieved pressure in fluid communication.

16. The device of claim 15 including a plurality of tie bolts received in axially-extending bores for urging said internally-toothed member and said first and second plate members toward tight fluid sealing engagement.

17. The device of claim 16 wherein said fluid passage means comprises a clearance between each of said axially-extending bores andsaid tie bolt received therein.

18. A hydraulic motor, comprising:

a. a housing having a high pressure fluid port and a low pressure fluid port;

b. an internally-toothed member having first and second axial end faces thereon and an externallytoothe'd member. eccentrically disposed within said internally-toothed member for orbital and rotational movement relative thereto; the teeth of said toothed members interengaging to define a plurality of expanding and contracting volumechambers during said relative movement;

c. valve means including a rotatable valve member connected for synchronous movement with one of said movements of said extemallytoothed member to provide fluid communication between said expanding volume chambers and one of said fluid ports and between said contracting volumechambers and the other of said fluid ports in response to said relative movement;

d. a valve port plate disposed between said valve member and said toothed members, said port plate having an axial end face in engagement with said first axial end of said internally-toothed member over a major portion thereof, said end faces defining a generally circular first seal ring groove therebetween;

e. said port plate end face and said firstaxial end face cooperating to define a first plurality of pressure relief areas disposed radially between said volume chambers and said seal ring groove and being in fluid communication with said 'seal ring groove and said low pressure fluid port; and 4 f. said port plate end face and said first axial end face defining a first fluid sealing land disposed radially between said volume chambers and said pressure relief areas to reduce the area subjected to pressure resulting from a pressure drop caused by fluid leaking from said high pressure in said volume chambers to said low pressure in said pressure relief areas across said sealing land in'a radially outward direction, said first fluid sealing land being relatively narrower in a radial directionthan said pressure relief areas.

19. The hydraulic motor of claim 18 including: a

a. a wear plate having'an axial end face in engagement with said second axial end face of said internallytoothed member over a major portion thereof, said end faces defining a generally circular second seal ring groove therebetween; 1 r

b. said wear plate end face and said second axial end face cooperating to define a second plurality of pressure relief areas disposed radially between said volume chambers and said second seal ring groove and being in fluid communication with said seal ring groove, said first plurality of pressure relief areas and said low pressure fluid port; and

c. said wear plate end face and said second axial end face defining a second fluid sealing land disposed radially between said volume chambers and said second plurality of pressure relief areas.

20. The hydraulic motor of claim 18 wherein each of said plurality of pressure relief areas is disposed radially outward from and adjacent to one of said volume chambers and is disposed circumferentially between adjacent teeth of said intemally-toothed member.

21. The hydraulic motor of claim 18 wherein said internally-toothed member is maintained in fixed, sealing engagement with said valve port plate by means of a plurality of tie bolts extending axially at least through said internallytoothed member and said port plate.

22. The hydraulic motor of claim 18 wherein the total of said plurality of pressure relief areas is relatively greater than the area of said fluid sealing land to .r .outlet ports and afluidexhaust port;

"c. said endcap member end substantially reduce the area, over which pressurized fluid between saida engaging end faces ,exerts a force tending to, separate. said end faces.

23. A fluid servo-control device, comprising; a. a housing having a fluid inlet port, a pair of fluid b, an internallyetoothedrrnember having first and second axial endfaces thereon and an externallytoothed membereccentrically disposed Within said internally-toothed member for orbital and rotational movement relative thereto to define a pluralityof expandingand contracting fluid volume metering chambers during said-relative movement; 0. valve means including a rotary input valve member and a follow-upvalve member, saidfollow-up valve member beingconnected for synchronous movement with one of said movements of said externally-toothed member for' selectively porting fluid from said inlet port to said expanding metering 1 chambers and from said contracting metering.

chambers to one of said outlet ports in responseto rotation of said input valve member;v

. d. a port plate disposed between'said internally.-

toothed memberand said valve means, said port plate having anaxial end face in. engagement with said first axial end face of said internally-toothed member over a major portion-thereof, said end faces defining ,a generally circular first seal ring groove therebetween; v

c. said port plate end face and said first axial end face cooperating to define a firstfluidically continuous pressure relief groove disposedradially between said metering chambersand said seal ring groove and being in fluid communication with said seal ring groove and. said'fluid exhaust port; and i i .f. said port plate end face and said first axial end face defining a first fluid sealing land disposed radially a. an endcap member having an axial end face in engagementwith said second axial end face of said internallytoothed member over a major portion I thereof, said end faces defining a generally circular second seal ring groove therebetween;

b, said endcap member end face and said second axial end face Cooperating to define a second fluidically continuous pressure relief groove disposed radially between said metering chambers and said .s econd seal ring groove, and being in fluid communication said second seal ring groove, said first pressure, relief groove and said fluid "exhaust port; iand face said second axial end face defining a second fluid sealing land disposed radially between said, metering chambers and said second pressure relief groove. 25. The control device of claim 23 wherein said internally-toothed n1ember is maintained in fixed, sealing ate to define a pressure relief area in fluid communication with said fluid exhaust port to reduce the area subjected to leakage pressure tending to separate said extemally-toothed member and said wear plate.

27. The control device of claim 23 wherein said fluid sealing land is contoured to follow substantially the outer periphery of said metering chambers. 

1. A rotary fluid pressure device, comprising: a. a housing having a fluid inlet port and a fluid outlet port and defining at least a first surface therein; b. an internally-toothed member and an externallytoothed member eccentrically disposed within said internally-toothed member for relative orbital and rotational movement therebetween, the teeth of said members interengaging to define a plurality of expanding and contracting volume chambers during said relative movement; c. valve means; d. means connecting said valve means for synchronous movement with one of said movements of said toothed members, said valve means being operable upon said synchronous movement to connect one of said ports in fluid communication with said expanding volume chambers and the other of said ports in fluid communication with said contracting volume chambers; e. said toothed members having first axial end faces abuttingly engaging said first housing surface, said housing surface and one of said first axial end faces cooperating to define a first sealing land radially adjacent said volume chambers and at least one area of relieved pressure, including a fluidicly continuous groove, said sealing land being disposed radially between said volume chambers and said area of relieved pressure; f. said area of relieved pressure being at least about as wide in a radial direction as said sealing land; and g. passage means disposed within said housing for connecting said relieved area in open communication with one of said ports to reduce the area subjected to fluid pressure tending to separate said faces from said surface during operation of said device.
 2. The device of claim 1 wherein said sealing land has a generally constant width and is substantially continuous circumferentially about said first housing surface.
 3. The device of claim 1 including a plurality of circumferentially spaced apart areas of relieved pressure, the total of said relieved areas being relatively greater than the area of said sealing land.
 4. The device of claim 1 wherein said fluidicly continuous groove comprises a seal ring groove and sealing means disposed therein, said sealing land being disposed radially between said volume chambers and said seal ring groove.
 5. The device of claim 1 including a generally circular seal ring groove disposed generally concentric with said fluidicly continuous groove.
 6. The device of claim 1 wherein: a. said housing defines a second surface therein, said first and second surfaces being substantially parallel and oppositely disposed about said toothed members; and b. said toothed members having second axial end faces abuttingly engaging said second housing surface, said housing surface and one of said axial end faces cooperating to define a second sealing land radially adjacent said volume chambers and at least one second area of relieved pressure, said second sealing land being disposed radially between said volume chambers and said second relieved area.
 7. The device of claim 6 wherein said first and second relieved areas are in open communication.
 8. A rotary fluid pressure device, comprising: a. a housing having a fluid inlet port and a fluid outlet port; b. an internally-toothed member having first and second axial end faces thereon and an externally-toothed member eccentrically disposed within said internallytoothed member for orbital and rotational movement relatiVe thereto, the teeth of said members interengaging to define a plurality of expanding contracting volume chambers during said relative movement; c. valve means operable between said inlet port and said outlet port for selectively porting fluid to and from said volume chambers as said chambers alternately expand and contract in response to said relative movement; d. means connecting said valve means for synchronous movement with one of said movements of said toothed members; e. a first plate member having an axial end face in engagement with said first axial end face of said internally-toothed member over a major portion thereof; f. said plate member end face and said first axial end face cooperating to define a first sealing land disposed radially outward from and adjacent to said volume chambers and at least one area of relieved pressure including a fluidicly continuous groove disposed radially outward from and adjacent to said sealing land; g. said area of relieved pressure being at least about as wide in a radial direction as said sealing land; and h. passage means disposed within said housing for venting said relieved area to reduce the pressure therein, to thereby reduce the force tending to separate said end faces during pressurization of said volume chambers.
 9. The device of claim 8 wherein said fluidicly continuous groove comprises a seal ring groove and sealing means disposed therein.
 10. The device of claim 8 including a generally circular seal ring groove, said fluidicly continuous groove being generally circular and disposed concentric with said seal ring groove.
 11. The device of claim 8 including a plurality of said area of relieved pressure, each of said areas being disposed radially outward from and adjacent to one of said volume chambers and disposed circumferentially between adjacent teeth of said internally-toothed member.
 12. The device of claim 11 wherein the total of said relieved areas is relatively greater than the area of said sealing land to minimize the area over which leakage of pressurized fluid can exert a force tending to separate said engaging end faces.
 13. The device of claim 12 wherein said sealing land has a generally constant width and is substantially continuous circumferentially about said internally-toothed member.
 14. The device of claim 8 including: a. a second plate member having an axial end face in engagement with said second axial end face of said internally-toothed member over a major portion thereof; b. said second plate member end face and said second axial end face cooperating to define a second sealing land disposed radially outward from and adjacent to said volume chambers and at least one second area of relieved pressure radially outward from and adjacent to said sealing land; and c. said relieved area being in fluid communication with said passage means.
 15. The device of claim 14 wherein a plurality of fluid passage means extend axially through said internally-toothed member interconnecting said first and second areas of relieved pressure in fluid communication.
 16. The device of claim 15 including a plurality of tie bolts received in axially-extending bores for urging said internally-toothed member and said first and second plate members toward tight fluid sealing engagement.
 17. The device of claim 16 wherein said fluid passage means comprises a clearance between each of said axially-extending bores and said tie bolt received therein.
 18. A hydraulic motor, comprising: a. a housing having a high pressure fluid port and a low pressure fluid port; b. an internally-toothed member having first and second axial end faces thereon and an externally-toothed member eccentrically disposed within said internally-toothed member for orbital and rotational movement relative thereto, the teeth of said toothed members interengaging to define a plurality of expanding and contracting volume chambers during said relative movement; c. valve means including a rotatable valve member connected for synchronous movement with one of said movements of said externallytoothed member to provide fluid communication between said expanding volume chambers and one of said fluid ports and between said contracting volume chambers and the other of said fluid ports in response to said relative movement; d. a valve port plate disposed between said valve member and said toothed members, said port plate having an axial end face in engagement with said first axial end of said internally-toothed member over a major portion thereof, said end faces defining a generally circular first seal ring groove therebetween; e. said port plate end face and said first axial end face cooperating to define a first plurality of pressure relief areas disposed radially between said volume chambers and said seal ring groove and being in fluid communication with said seal ring groove and said low pressure fluid port; and f. said port plate end face and said first axial end face defining a first fluid sealing land disposed radially between said volume chambers and said pressure relief areas to reduce the area subjected to pressure resulting from a pressure drop caused by fluid leaking from said high pressure in said volume chambers to said low pressure in said pressure relief areas across said sealing land in a radially outward direction, said first fluid sealing land being relatively narrower in a radial direction than said pressure relief areas.
 19. The hydraulic motor of claim 18 including: a. a wear plate having an axial end face in engagement with said second axial end face of said internallytoothed member over a major portion thereof, said end faces defining a generally circular second seal ring groove therebetween; b. said wear plate end face and said second axial end face cooperating to define a second plurality of pressure relief areas disposed radially between said volume chambers and said second seal ring groove and being in fluid communication with said seal ring groove, said first plurality of pressure relief areas and said low pressure fluid port; and c. said wear plate end face and said second axial end face defining a second fluid sealing land disposed radially between said volume chambers and said second plurality of pressure relief areas.
 20. The hydraulic motor of claim 18 wherein each of said plurality of pressure relief areas is disposed radially outward from and adjacent to one of said volume chambers and is disposed circumferentially between adjacent teeth of said internally-toothed member.
 21. The hydraulic motor of claim 18 wherein said internally-toothed member is maintained in fixed, sealing engagement with said valve port plate by means of a plurality of tie bolts extending axially at least through said internallytoothed member and said port plate.
 22. The hydraulic motor of claim 18 wherein the total of said plurality of pressure relief areas is relatively greater than the area of said fluid sealing land to substantially reduce the area over which pressurized fluid between said engaging end faces exerts a force tending to separate said end faces.
 23. A fluid servo-control device, comprising: a. a housing having a fluid inlet port, a pair of fluid outlet ports and a fluid exhaust port; b. an internally-toothed member having first and second axial end faces thereon and an externally-toothed member eccentrically disposed within said internally-toothed member for orbital and rotational movement relative thereto to define a plurality of expanding and contracting fluid volume metering chambers during said relative movement; c. valve means including a rotary input valve member and a follow-up valve member, said follow-up valve member being connected for synchronous movement with one of said movements of said externally-toothed member for selectively porting fluid from said inlet port to said expanding metering chambers and from said contracting metering Chambers to one of said outlet ports in response to rotation of said input valve member; d. a port plate disposed between said internally-toothed member and said valve means, said port plate having an axial end face in engagement with said first axial end face of said internally-toothed member over a major portion thereof, said end faces defining a generally circular first seal ring groove therebetween; e. said port plate end face and said first axial end face cooperating to define a first fluidically continuous pressure relief groove disposed radially between said metering chambers and said seal ring groove and being in fluid communication with said seal ring groove and said fluid exhaust port; and f. said port plate end face and said first axial end face defining a first fluid sealing land disposed radially between said metering chambers and said pressure relief groove to reduce the area subjected to pressure resulting from a pressure drop caused by fluid leaking from said metering chambers to said pressure relief groove across said sealing land in a radially outward direction, said pressure relief groove being approximately as wide in a radial direction as said first fluid sealing land over at least a substantial circumferential portion of said pressure relief groove.
 24. The control device of claim 23 including: a. an endcap member having an axial end face in engagement with said second axial end face of said internallytoothed member over a major portion thereof, said end faces defining a generally circular second seal ring groove therebetween; b. said endcap member end face and said second axial end face cooperating to define a second fluidically continuous pressure relief groove disposed radially between said metering chambers and said second seal ring groove, and being in fluid communication with said second seal ring groove, said first pressure relief groove and said fluid exhaust port; and c. said endcap member end face and said second axial end face defining a second fluid sealing land disposed radially between said metering chambers and said second pressure relief groove.
 25. The control device of claim 23 wherein said internally-toothed member is maintained in fixed, sealing engagement with said port plate by means of a plurality of tie bolts extending axially at least through said internally-toothed member and said port plate.
 26. The control device of claim 23 wherein said externally-toothed member has an axial end face, substantially planar with said first axial end face of said internally-toothed member, and said externally-toothed member end face and said port plate end face cooperate to define a pressure relief area in fluid communication with said fluid exhaust port to reduce the area subjected to leakage pressure tending to separate said externally-toothed member and said wear plate.
 27. The control device of claim 23 wherein said fluid sealing land is contoured to follow substantially the outer periphery of said metering chambers. 